Mr. Kelly’s evaluation confirms what legal analysts on both sides of the issue told The Washington Times last month, after Texas said it would force a confrontation over the 2012 program, known as Deferred Action for Childhood Arrivals, which President Obama began and Mr. Kelly and President Trump have continued.

Meeting with the Congressional Hispanic Caucus, Mr. Kelly said final decisions about whether to defend DACA lie with the Justice Department and Attorney General Jeff Sessions, but the secretary said the lawyers he’s spoken with don’t believe it would withstand a legal test.

His comments came the same day that a House subcommittee gave initial approval for the first down payment on Mr. Trump’s border wall.

The $ 1.6 billion included in the annual homeland security spending bill would construct 60 miles of new wall in Texas, as well as replace fencing in San Diego.

The spending bill also included money for 1,000 new deportation agents and officers and a total of 44,000 detention beds, which should help Mr. Trump make good on his promise of stiffer enforcement in the interior of the U.S.

Democrats resisted the additional money, but the bill cleared the panel on a voice vote. It now heads to the Appropriations Committee, en route to the full House floor.

Combined with Mr. Kelly’s words in the private meeting, Democrats said they fear a looming crackdown.

“This was a wake-up call that Trump, Sessions and Kelly are serious about mass deportation and are anxious to get started,” said Rep. Luis V. Gutierrez, Illinois Democrat. “It is a call to action for people who oppose mass deportation and turning the documented into undocumented so that they can be deported.”

David Lapan, a spokesman for Mr. Kelly, said the secretary didn’t mention mass deportations in the meeting, and has categorically ruled them out as a practice for his department.

Nearly 800,000 Dreamers are currently protected under the DACA program. Another 200,000 are shielded from deportation under a humanitarian program, Temporary Protected Status, after natural disasters struck their home countries — in some cases nearly two decades ago.

Texas Attorney General Ken Paxton has said that unless the Trump administration revokes DACA, he’ll go back to the same court that blocked a broader amnesty, the 2014 Deferred Action for Parents of Americans program, and ask the judge to block DACA as well. Legal scholars say there’s no substantive difference between the two programs when it comes to the law.

Mr. Kelly has said he would continue issuing permits under the DACA program, though he said the legal battle rests with Mr. Sessions.

Mr. Kelly has also said he’s skeptical of repeated renewals of TPS, which he said were done under previous administrations without the sort of careful review of facts on the ground. He has signaled that those sorts of automatic renewals are a thing of the past.

The newly minted secretary, a former Marine general, has said it’s up to Congress to solve the big issues involved in immigration. He has said that if lawmakers want permanent legal status for Dreamers or longtime TPS recipients, they should pass legislation.

Mr. Gutierrez, though, said Mr. Kelly could choose a middle-ground, announcing — as the Obama administration did — that he won’t target those illegal immigrants for deportation.

“I told him straight up that he could prevent the August deportation of Francisca Lino — the wife of a U.S. citizen and mother of U.S. citizen children in Chicago — just by picking up the phone. And he seemed not to know he has that power,” the congressman said.

“He either does not understand his authority under current law, or was stonewalling, or doing a very convincing job of playing dumb. Or maybe some combination of the three,” Mr. Gutierrez concluded.